1. Field of the Invention
This invention generally relates to an image processing system and method, and, in particular, to an image processing system for processing an image having both letter and photographic information to extract the letter information therefrom.
2. Description of the Prior Art
In an image processing system, such as a facsimile machine or image processor, it is often the case to require to handle an original document having both of a binary-valued image, such as characters and symbols and generically referred to as letter information hereinafter, and a continuously varying tone image, such as photographic or graphic information. In such a case, if only the letter information can be extracted from the image signal obtained by optically reading a composite original having both of letter and photographic information, an optimal image processing technique, such as data compression, can be applied to the letter information, thereby allowing to enhance the performance of an image processing system. There has been proposed to discriminate the letter region from the photographic region based on the distribution of run-lengths which are obtained by thresholding an optically read image signal with a predetermined threshold level; however, this technique is not reliable and an accurate discrimination cannot be expected at all times.